Study On Windbreak And Sand Fixation Effect Of Biodegradable Poly Lactic Acid (PLA) Sand Barrier In Urumqi Sandy Land

Under the background of human disturbance and natural environment deterioration,the ecological environment of Urumqi Sandy Land has been degraded and the sand area has been further expanded.Mechanical sand barrier sand fixation is the first measure of sand control and the prerequisite and necessary condition for vegetation restoration.PLA sand barrier is a kind of biodegradable polylactic acid fiber green mechanical sand barrier,and its wind and sand resistance effect research has important practical significance in practical application.In this study,Xingaowle County,which has fragile ecological environment and serious wind and sand hazards in Urumqi Sandy Land,was taken as the Study area.The wind speed,sediment transport and soil mechanical composition of PLA sand barriers of different specifications（sand barriers of 0.5 m×0.5 m,1 m×1 m,2 m×2 m and 3 m×3 m）were quantitatively analyzed,and the wind speed flow field characteristics,wind sand transport characteristics,sediment particle size characteristics and near-surface erosion and accumulation rules of PLA sand barriers of different specifications were clarified.The windproof and sand-blocking effect of PLA sand barrier of different specifications and its mechanism were revealed.The main conclusions are as follows:（1）When the size of sand barrier is less than 3 m×3 m,the wind speed profile shows an’S’shaped variation trend.The surface roughness of PLA sand barrier of different specifications is as follows:1 m×1 m>0.5 m×0.5m>2 m×2 m>3 m×3 m>bare sand.After the PLA sand barrier was laid,The sediment transport of four types of sand barriers decreased between 38.72%and 75.69%;the sediment transport within 10 cm height accounted for 70.59～94.71%of the total sediment transport.The sediment transport rate in the PLA sand barrier showed a good exponential relationship with the height（R²>0.77）;after the PLA sand barrier was laid,the sand flow structure changed,the fine sand content increased by 4.56%,while the medium sand content decreased by 11.94%.Sand barrier can effectively reduce the near-surface wind speed and change wind-sand flow structure.（2）After paving the sand barrier,The content of fine sand particles in the sand barrier increased by 19.54%,while that of coarse sand and ultra coarse sand get deceased from 99.4%to 67.58%,surface sediment particles become finer;the average grain size of sediment soil in the sand barrier is larger than that in bare sand.The sorting ability of 1 m×1 m,2 m×2 m and 3m×3 m is higher than that of bare sand,and without obvious change in the kurtosis.The sediment in the sand barrier presents a negative bias,which is lower than bare sand.The distribution of sediment particles in PLA sand barrier was more uniform,and there was fine granulation.（3）The wind erosion depth in the center of the concave surface of sand barrier increase by 16.06 cm along with the enlargement of sand barrier specification,while the sediment strength decreases by 3.44 g·cm^-3along with the enlargement of sand barrier specification.The sediment in the barrier grids become wind erosion.The coefficient of erosion is stable at 1/9～1/8,and it decreases with the increase of sand barrier size.The most deep point of wind erosion in the barrier grids shifts along with major wind direction,and the degree of wind erosion that is consistent with major wind direction in the barrier grids is greater.Within the study area,the wind erosion mostly happens at the directions of NW-SE and W-E,and the concave surface formed at the top of slope is more stable,where is suitable for paving PLA sand barrier with specification of 1m×1 m and 2 m×2 m.